Process for production of polyarylene sulfide

ABSTRACT

There is provided a method for producing a poly(arylene sulfide) in which a dihalo-aromatic compound and an alkali metal halide are polymerized by heating in an organic amide solvent, wherein the cooling time for the polymerization reaction system is significantly reduced. After the polymerization process, there is provided a cooling process for cooling the polymerization reaction system comprising a liquid phase containing the product poly (arylene sulfide) and the organic amide solvent and a vapor phase containing a gas component (A); and in the cooling process, the gas component (A) in the vapor phase is cooled while the content of a low boiling gas component (A 1 ), which has a lower boiling point than water and exists in the gas component (A), is reduced in the vapor phase of the polymerization system.

TECHNICAL FIELD

[0001] The present invention relates to a method for producing apoly(arylene sulfide) (hereinafter abbreviated as “PAS”), and moreparticularly to a method for efficiently and economically producing aPAS by rapidly cooling a polymerization reaction system after apolymerization process of the PAS.

BACKGROUND ART

[0002] A PAS typified by polyphenylene sulfide (hereinafter abbreviatedas “PPS”) is an engineering plastic excellent in heat resistance,chemical resistance, flame retardancy, mechanical strength, electricalproperties, dimensional stability and the like. The PAS can be molded tovarious moldings, films, sheets, fibers and the like by typical meltprocessing methods such as extrusion molding, injection molding,compression molding and the like. In addition, the PAS can be used forcoatings on other materials such as metal. Therefore, the PAS is used inwide application fields such as electric and electronic equipment andautomobile equipment.

[0003] A PAS is generally produced by a method in which adihalo-aromatic compound and an alkali metal sulfide are polymerized(polycondensed) by heating in an organic amide solvent. A polymerizationaid, a phase separation agent or the like is added as required beforethe polymerization process, during the polymerization process or afterthe polymerization process.

[0004] Various additional processes are provided before and after thepolymerization process of PAS. The polycondensation reaction of adihalo-aromatic compound and an alkali metal sulfide is susceptible towater, but the alkali metal sulfide as a raw material contains muchamount of water such as the water of crystallization in many cases.Therefore, before the polymerization process of PAS, there is generallyprovided a dehydration process in which the water in the reaction systemis adjusted by distilling water out of a mixture containing an organicamide solvent and an alkali metal sulfide. After the polymerizationprocess, there is provided a process in which the polymerizationreaction system is cooled and the PAS produced is recovered from thepolymerization reaction system.

[0005] Since the polycondensation reaction between a dihalo-aromaticcompound and an alkali metal sulfide is a salt elimination reaction, alarge amount of alkali metal halides (for example, NaCl) is formed as aby-product. In a recovery process, a reaction mixture containing the PASproduced and a large amount of byproducts is filtered, and then aresultant solid matter is washed to remove byproducts or oligomers mixedin or attached to the PAS. The thus recovered PAS is dried in a dryingprocess. Further, there is also provided a process to recover an organicamide solvent, an unreacted monomer and the like.

[0006] In the initial stage of the development of PAS, there has beenadopted a method of rapid cooling by removing a solvent by a solventflashing process from a polymerization reaction system that is heated tohigh temperatures and in a high-pressure state, after the polymerizationprocess. However, it is difficult to remove the byproducts and oligomersfrom the PAS by operations such as filtration and washing because thePAS is precipitated as fine powders, in the solvent flashing process.Further, the powdered PAS is difficult in handling and measurement.

[0007] Therefore, at present, there is adopted a method in which aslurry containing a granular PAS is formed by reducing the temperatureof the reaction mixture containing an organic solvent, a PAS, abyproduct, a phase separation agent and the like, wherein the PAS is ina molten state, after the polymerization process. The phase separationagent has an effect to induce liquid-liquid phase separation in thereaction mixture in a high-temperature state, producing an organic amidesolvent phase and a molten PAS phase. Organic carboxylic acid salts,water and the like are used as the phase separation agent. According tothis method, a granular PAS can be recovered. The granular PAS is easyin separation of byproducts and oligomers and excellent in handling andmeasurement.

[0008] However, a method for reducing the temperature of a reactionmixture in a high-temperature state after a polymerization processrequires a long cooling process, so the method has problems that theproduction efficiency is low and it is not economical. Therefore,several methods are proposed in order to produce a high-purity granularPAS in a relatively short cooling time.

[0009] Japanese Patent Laid-Open No. 2001-89569 proposes a method inwhich a polyhalogenated aromatic compound and a sulfidizing agent aresubjected to polymerization reaction in a temperature range of 245 to290° C., and then the reaction mixture is cooled in a two-step coolingrate in a cooling process. Specifically, it proposes a method in whichthe reaction mixture is first cooled at a cooling rate of 0.2 to 1.3°C./minute and, after reaching a specific temperature, at a cooling rateof higher than 1.3° C./minute. Its example shows an experimental examplein which the reaction mixture was cooled at a cooling rate of 1°C./minute to 198° C. and then at a cooling rate of 2° C./minute to 50°C. The above patent describes that the method has provided a highly purePAS in a short polymerization process time. However, this method cannotsignificantly reduce the cooling time.

[0010] Japanese Patent Laid-Open No. 10-87831 proposes a method forproducing a granular PPS in which a sulfur source and apolyhalo-aromatic compound are subjected to polymerization reaction inan organic polar solvent in a sealed vessel and the reaction mixture isgradually cooled in the later stage of the polymerization reaction.According to the production method, the reaction mixture is graduallycooled in the later stage of the polymerization reaction, and thepressure of the vessel is relieved in a state where at least 50% by molerelative to the charged sulfur source of the polymer exists as a solidgranular polymer and the pressure within the sealed vessel is 0.39×10⁶Pa or higher. Thus, a polymerization reaction mixture composed of a gasphase and a liquid phase is degassed and the pressure within the vesselis reduced. The above patent also describes that liquid-liquid phaseseparation is induced in a liquid phase component before cooling. Thiscooling method requires a gradual cooling, for example, at a coolingrate of about 1° C./minute, so it is difficult to substantially reducethe cooling time. Further, when the amount of water to be evaporated outof the gas phase by the degassing is large, this method requires adegassing time corresponding to the large amount of water.

[0011] Japanese Patent Laid-Open No. 09-296042 proposes a method forproducing a PAS by reacting a dihalo-aromatic compound with asulfidizing agent in an organic polar solvent. In the method, after thecompletion of the reaction, water is removed from a reaction slurry at atemperature lower than the temperature at the completion of the reactionand higher than the temperature where a polymer is precipitated, andthen the reaction slurry is cooled to precipitate the polymer. Theexample in the above patent describes that after the completion of thereaction, the reaction mixture is cooled from 250° C. to 230° C. in 10minutes; a water-NMP (N-methyl-2-pyrolidone) mixture is evaporated in 30minutes while maintaining this temperature; and then the reactionmixture is cooled at a rate of 1° C./minute to 150° C. However, thismethod requires that water needs to be evaporated while maintaining thetemperature where PPS is not precipitated, and also the reaction mixtureneeds to be gradually cooled at a cooling rate of 1° C./minute.

[0012] Japanese Patents No. 2604673 and No. 2604674 propose a method forproducing a PAS by reacting an alkali metal sulfide with adihalo-aromatic compound in an organic amide solvent, wherein a liquidphase is heated to a temperature exceeding the temperature of the liquidphase under the atmospheric pressure and a vapor phase part in a closedreactor is cooled, thereby condensing part of the vapor phase in thereactor and refluxing the condensate back into the liquid phase.

[0013] The method described in these patents is intended to return alarge amount of reflux with a high water content back into the upperpart of a liquid phase to form a layer with a high water content and toallow the layer to contain a residual alkali metal sulfide, ahalogenated alkali metal, an oligomer and the like in the liquid phase.Therefore, this method is not a method for cooling a polymerizationreaction system containing a liquid phase. These patents describe thatduring the cooling of the upper part of a reactor, a liquid temperatureis maintained constant so that it is not reduced. Actually, cooling of avapor phase only by this method cannot effectively cool the entirepolymerization reaction system containing a liquid phase.

DISCLOSURE OF THE INVENTION

[0014] It is an object of the present invention to provide a method forefficiently and economically producing a poly(arylene sulfide) byrapidly cooling a polymerization reaction system after a polymerizationprocess of the poly(arylene sulfide).

[0015] More specifically, it is an object of the present invention toprovide a method for producing a poly(arylene sulfide) in which adihalo-aromatic compound and an alkali metal sulfide are polymerized byheating in an organic amide solvent, wherein after a polymerizationprocess, there is provided a cooling process for cooling apolymerization reaction system comprising a liquid phase containing thepoly(arylene sulfide) produced and the organic amide solvent and a vaporphase containing a gas component, and the cooling process can beeffectively implemented.

[0016] After the polymerization process, the polymerization reactionsystem comprising a liquid phase and a vapor phase is in ahigh-temperature and high-pressure state in a closed polymerizer. Theliquid phase contains an organic amide solvent, a PAS produced, ahalogenated alkali metal, additives such as a phase separating agent andthe like. The vapor phase contains hydrogen sulfide, water (watervapor), an organic amide solvent (vapor), a dihalo-aromatic compound(vapor) various thermally decomposed products and the like. If thepolymerizer is purged with nitrogen before starting polymerization, alarge amount of nitrogen will be contained in the vapor phase. A methodin which the polymerization reaction system is stopped heating andgradually cooled after the polymerization process requires a long timefor cooling.

[0017] Water vapor is contained in a vapor phase. When the water vaporis condensed and the condensate (water) is refluxed back into a liquidphase, the condensate is heated by a high-temperature liquid phase andis re-evaporated. Since the latent heat of evaporation of water at there-evaporation is high, it may be considered that the liquid phase canbe efficiently cooled. However, as the vapor phase contains a largeamount of low boiling gas components such as hydrogen sulfide, nitrogenand alkyl mercaptans, it is not efficient to cool the gas component inthe vapor phase to condense part of the gas component such as watervapor and reflux it.

[0018] The above described Japanese Patents No. 2604673 and No. 2604674disclose a method for cooling the vapor phase part of a reactor isdisclosed. Specifically, part of the vapor phase is condensed and thecondensate is refluxed back into a liquid phase by cooling to a very lowtemperature, such as cooling by passing a coolant having a temperatureof 20° C. through a coil wound around the upper part of the reactor.However, the method described in these patents is not adopted as acooling method. In addition, it is not efficient as a method forcondensing water vapor and the like contained in the vapor phase.Further, if the temperature of the upper part of the reactor is reducedtoo much, high-melting point substances such as a dihalo-aromaticcompound contained in the vapor phase may deposit on the inner wall ofthe upper part of the reactor.

[0019] As a result of an intensive study to achieve the above describedobject, the inventors have hit upon a method in which in a coolingprocess, a gas component in a vapor phase is cooled and at the same timea low boiling gas component with a lower boiling point than water in thegas component is exhausted from the vapor phase of a polymerizationreaction system, thereby reducing the content thereof.

[0020] It has been found that if the content of a low boiling gascomponent in a vapor phase is reduced, a high boiling gas componentcontaining water vapor and the like can be efficiently condensed and thecondensate can be refluxed back into a polymerization reaction system,for example, by cooling the gas component using a reflux condenser.Thus, when the condensate refluxed back into the polymerization reactionsystem is introduced into a liquid phase by dropping it on the liquidphase or the like and at least part of the condensate introduced intothe liquid phase is re-evaporated, the entire polymerization reactionsystem including the liquid phase can be extremely efficiently cooled bya high latent heat of evaporation.

[0021] According to the method of the present invention, a high boilinggas component can be efficiently condensed and refluxed withoutsubstantially reducing the temperature of the coolant to be passedthrough a jacket of a reflux condenser, and the entire polymerizationreaction system including a liquid phase can be rapidly cooled byutilizing the latent heat of evaporation required when the water and thelike refluxed back into the liquid phase is re-evaporated. The presentinvention has been completed based upon these findings.

[0022] The present invention provides a method for producing apoly(arylene sulfide) in which a dihalo-aromatic compound and an alkalimetal sulfide are polymerized by heating in an organic amide solvent,which comprises:

[0023] (1) after a polymerization process, providing a cooling processfor cooling a polymerization reaction system comprising a liquid phasecontaining the poly(arylene sulfide) produced and the organic amidesolvent and a vapor phase containing a gas component (A) and

[0024] (2) in the cooling process, cooling the gas component (A) in thevapor phase and reducing the content of a low boiling gas component(A1), which has a lower boiling point than water and exists in the gascomponent (A), in the vapor phase of the polymerization system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is a sectional view showing a method for cooling a gascomponent in a vapor phase of a polymerization reaction system, using areflux condenser.

BEST MODE FOR CARRYING OUT THE INVENTION

[0026] 1. Method for Polymerizing Poly(Arylene Sulfide)

[0027] Poly(arylene sulfide)s (PAS) can be synthesized by heating topolymerize dihalo-aromatic compounds and alkali metal sulfides inorganic solvents. A polymerization reaction system can be added withphase separating agents, polymerization aids and the like as necessary.

[0028] (1) Alkali Metal Sulfide

[0029] Alkali metal sulfides used in the present invention includelithium sulfide, sodium sulfide, potassium sulfide, rubidium sulfide,cesium sulfide and mixtures of two or more thereof. These alkali metalsulfides can be used as hydrates, aqueous mixtures or anhydrides.Typical alkali metal sulfides such as sodium sulfide are generallycommercially available as hydrates. The hydrates include, for example,sodium sulfide nonahydrate (Na₂S.9H₂O) and sodium sulfide pentahydrate(Na₂S.5H₂O). The alkali metal sulfides can also be prepared by in situreaction of alkali metal hydrosulfides with alkali metal hydroxides inorganic amide solvents.

[0030] Since a trace quantity of alkali metal hydrosulfides or alkalimetal thiosulfates may be present in alkali metal sulfides asimpurities, these trace components may be removed or converted to alkalimetal sulfides by adding alkali metal hydroxides.

[0031] Among alkali metal sulfides, sodium sulfide and sodiumhydrosulfide are particularly preferred in that they are less expensive.

[0032] In a process for producing PAS, when a large amount of water ispresent such as the water of hydration of alkali metal sulfides, watermedia in aqueous mixtures and the water by-produced from a reaction ofalkali metal hydrosulfides with alkali metal hydroxides, the water isdehydrated in a dehydration process before a polymerization process.

[0033] (2) Dihalo-Aromatic Compound

[0034] The dihalo-aromatic compounds used in the present invention arethose dihalo-aromatic compounds with two halogen atoms directly bondedto an aromatic ring. The dihalo-aromatic compounds include, for example,o-dihalobenzenes, m-dihalobenzenes, p-dihalobenzenes, dihalotoluenes,dihalonaphthalenes, methoxy-dihalobenzenes, dihalobiphenyls,dihalobenzoic acids, dihalodiphenyl ethers, dihalodiphenyl sulfones,dihalodiphenyl sulfoxides and dihalodiphenyl ketones. A halogen atomdenotes each atom selected from fluorine, chlorine, bromine and iodine.Two halogen atoms in the same dihalo-aromatic compound may be the sameor different.

[0035] Specific examples of dihalo-aromatic compounds includep-dichlorobenzene, m-dichlorobenzene, 2,5-dichlorotoluene,p-dibromobenzene, 1,4-dichloronaphthalene,1-methoxy-2,5-dichlorobenzene, 4,4′-dichlorobiphenyl,3,5-dichlorobenzoic acid, 4,4′-dichlorodiphenyl ether,4,4′-dichlorodiphenyl sulfone, 4,4′-dichlorodiphenyl sulfoxide and4,4′-dichlorodiphenyl ketone. Among them, those mainly composed ofp-dihalobenzenes typified by p-dichlorobenzene are preferred.

[0036] Dihalo-aromatic compounds may have one or more substituents suchas carboxyl groups, hydroxy groups, nitro groups, amino groups andsulfonate groups. When they have a plurality of substituents, thesubstituents may be of a single type or of a combination of differenttypes. These dihalo-aromatic compounds can be used each independently orin combination of two or more. When two or more dihalo-aromaticcompounds are used, copolymers having two or more different structuralunits will be obtained. The copolymers include random copolymers, blockcopolymers and the like.

[0037] The dihalo-aromatic compounds are used in an amount of typicallyfrom 0.90 to 1.20 moles relative to one mole of charged alkali metalsulfides.

[0038] (3) Organic Amide Solvent

[0039] The present invention uses organic amide solvents as a solvent ina dehydration process, a polymerization process, a cooling process andthe like.

[0040] The organic amide solvents are preferably stable under a basiccondition at a high temperature. Specific examples of the organic amidesolvents include amide compounds such as N,N-dimethylformamide andN,N-dimethylacetamide; N-alkyl pyrrolidone compounds or N-cycloalkylpyrrolidone compounds such as N-methyl-ε-caprolactam,N-methyl-2-pyrrolidone (hereinafter abbreviated as “NMP”) andN-cyclohexyl-2-pyrrolidone; N,N-dialkyl imidazolidinone compounds suchas 1,3-dialkyl-2-imidazolidinones; tetraalkylurea compounds such astetramethylurea; and hexalkylphosphoric triamide compounds such ashexamethylphosphoric acid triamide. These organic amide solvents can beused each independently or in combination of two types or more.

[0041] Among these organic amide solvents, N-alkyl pyrrolidonecompounds, N-cycloalkyl pyrrolidone compounds and N, N-dialkylimidazolidinone compounds are preferred, and in particular NMP,N-methyl-ε-caprolactam and 1,3-dialkyl-2-imidazolidinones are morepreferred, NMP being most preferred.

[0042] The organic amide solvents used in the polymerization reaction ofthe present invention are used in an amount of typically from 0.1 to 10kg per mole of charged alkali metal sulfides.

[0043] (4) Additive Components

[0044] Monohalo compounds may be used in a small quantity in order toallow formation of the terminals of produced PASs and adjustpolymerization reaction and molecular weights. The monohalo compoundsmay be aromatic compounds or non-aromatic compounds.

[0045] In order to allow formation of branched or crosslinked polymers,polyhalo compounds to which 3 or more halogen atoms are bonded, activehydrogen-containing halogenated aromatic compounds, halogenated aromaticnitro compounds and the like can be used. Compounds other than aromaticcompounds may also be used as the polyhalo compounds as branching andcrosslinking agents, but aromatic compounds such as trihalobenzenes arepreferred.

[0046] Organic sulfonic acid metal salts, lithium halides, organiccarboxylic acid metal salts, alkali metal phosphates, alkaline earthmetal phosphates, alkali metal sulfates, alkaline earth metal oxides,alkaline earth metal hydroxides and the like can be used aspolymerization aids as appropriate. Many of these polymerization aidsare functional as phase separation agents.

[0047] (5) Phase Separation Agent

[0048] In the polymerization process of PAS, phase separation agents maybe contained in a reaction mixture so that polymerization reaction ispromoted and the PAS with a high degree of polymerization can beobtained in a short time. Phase separation agents are used to induceliquid-liquid phase separation in the reaction mixture (liquid phase) inwhich polymerization reaction has proceeded to some extent into twophases of a polymer-rich phase (molten PAS phase) and a polymer-poorphase (organic amide solvent phase). The phase separation agents may bepresent in the reaction mixture from the beginning of the polymerizationreaction, or may be added in the middle of the polymerization reaction.Further, the phase separation agents may be added to the reactionmixture after the completion of the polymerization reaction to form aliquid-liquid phase separation state, before cooling.

[0049] Specific examples of the phase separation agents include organicsulfonic acid metal salts, lithium halides, organic carboxylic acidmetal salts, alkali metal phosphates, alkaline earth metal phosphates,alkali metal sulfates and water, generally known as polymerization aidsfor PAS. These phase separation agents can be used not only singly, butalso in combination of two or more thereof. Among the phase separationagents, organic carboxylic acid metal salts such as lithium acetate andsodium acetate and water are preferred.

[0050] The phase separation agents are used in different amountsdepending on the type of compounds, and are used in an amount oftypically within the range from 0.01 to 10 moles relative to one mole ofcharged alkali metal sulfides.

[0051] (6) Dehydration Process

[0052] A dehydration process can be provided before a polymerizationprocess, in order to adjust water content in a reaction mixture. Thedehydration process is implemented by heating alkali metal sulfides inorganic amide solvents desirably under an inert gas atmosphere andseparating water outside the system by distillation. Alkali metalsulfides contain water exceeding the quantity required in thepolymerization process because they are typically used as hydrates oraqueous mixtures. In addition, when alkali metal hydrosulfides are usedas a sulfur source, approximately equimolar amount of alkali metalhydroxides are added, and they are reacted in situ in organic amidesolvents to be converted to alkali metal sulfides. This conversionreaction forms water as a by-product.

[0053] In the dehydration process, water including such hydrating water(water of crystallization), aqueous media and by-produced water ispartially eliminated into the required range of water content. In thedehydration process, the water content is reduced to a level where watercontent present in the polymerization process is generally from 0.3 to 5moles, preferably from 0.5 to 2.4 moles relative to one mole of thecharged alkali metal hydrosulfides. If in the dehydration process, theamount of water is reduced to a level lower than the above requirement,some water can be added before the polymerization process to adjust thewater content to a desired level.

[0054] These raw materials are charged at a temperature ranginggenerally from room temperature to 300° C., preferably from roomtemperature to 200° C. Apart of the raw materials may be added duringthe dehydration operation organic amide solvents are typically used asthe solvent in the dehydration process. The solvent to be used in thedehydration process is preferably the same organic amide solvent as usedin the polymerization process, most preferably NMP. The solvent is usedin an amount of generally from 0.1 to 10 kg per mole of charged alkalimetal sulfides.

[0055] The apparatus for use in the dehydration process may be the sameas the polymerization reaction apparatus (polymerizer) used in thepolymerization process, or may be different from it. The apparatus maybe of a batch process, a continuous process or a combination process ofthe both.

[0056] In the dehydration process, the charged mixture is heated at atemperature ranging generally 300° C. or less, preferably from 60 to280° C., for generally from 15 minutes to 24 hours, preferably from 30minutes to 10 hours. The method for heating includes a method formaintaining a constant temperature, a stepwise or a continuoustemperature-increasing method, or a method in which the both methods arecombined.

[0057] In the dehydration process, generally, part of the organic amidesolvent is evaporated together with water by azeotropy. Water isexhausted as an azeotropic mixture with the organic amide solvent, or aswater alone by separating the organic amide solvent and water bydistillation. Further, hydrogen sulfide is also evaporated together withwater or the azeotropic mixture of water and the organic amide solvent.The evaporated hydrogen sulfide is preferably recovered by anappropriate method such as a method in which it is absorbed into anaqueous alkali metal hydroxide solution, and reused as a sulfur source.

[0058] (7) Polymerization Process

[0059] In the polymerization process, a mixture containing the alkalimetal sulfide and organic amide solvent, prepared after the dehydrationprocess, is mixed with a dihalo-aromatic compound, and the resultantreaction mixture is then heated. The reaction mixture is prepared at atemperature ranging generally from 100 to 350° C., preferably from 120to 350° C. The order of the mixing is not particularly limited, and bothcomponents are added either partly by a small amount, or all at once.Further, a hydrogen sulfide-absorbing solution for recovering hydrogensulfide evaporated in the dehydration process may be mixed in anappropriate order. When the reaction mixture is prepared, the amount ofthe organic amide solvent or coexistent water may be adjusted, andfurther additives such as a polymerization aid and a phase separationagent may also be incorporated.

[0060] Thus, after the reaction mixture containing the organic amidesolvent, the alkali metal sulfide, the dihalo-aromatic compound and thelike is prepared, the reaction mixture is heated to subject the alkalimetal sulfide and the dihalo-aromatic compound to salt elimination andpolycondensation reactions. The polymerization reaction apparatus(polymerizer) is preferably of a material excellent in corrosionresistance that does not have an adverse effect such as decomposition onthe reaction mixture or reaction products. The reaction apparatus ispreferably composed of a titanium material for at least a wetted part.

[0061] The polymerization reaction, which proceeds by heating thereaction mixture in a polymerizer, is a thermal reaction in a closedsystem. The polymerization reaction may be performed under an inert gasatmosphere such as nitrogen, but the inert gas is not essential. Thepolymerization reaction of PAS is performed at a temperature generallyfrom 100 to 350° C., preferably from 150 to 330° C. However, the methodof the present invention is effective when the polymerization by heatingis performed at an elevated-temperature of preferably 180° C. or higher,more preferably 200° C. or higher, most preferably 240° C. or higher.

[0062] The method for heating includes a method for maintaining aconstant temperature, a stepwise or a continuous temperature-increasingmethod, or a method in which the both methods are combined. Thepolymerization reaction time is within the range of generally from 10minutes to 72 hours, preferably from 30 minutes to 48 hours. The organicamide solvent for use in the polymerization process is within the rangeof generally from 0.1 to 10 kg, preferably from 0.15 to 1 kg per mole ofcharged alkali metal sulfides. The quantity may be changed during thepolymerization reaction provided it is within this range.

[0063] The amount of coexistent water at the start of the polymerizationreaction is within the range of generally from 0.3 to 5 moles,preferably from 0.5 to 2.4 moles relative to one mole of charged alkalimetal hydrosulfides. In the preferred embodiment of the presentinvention, at any time from the start of polymerization to itscompletion, a phase separation agent can be added to produce a PAShaving a relatively high molecular weight. Water is particularlydesirable as the phase separation agent in terms of cost, ease ofremoval and the like.

[0064] When a liquid-liquid phase separation state is formed byincreasing the content of the phase separation agent, the phaseseparation agent can be added at any time from the start ofpolymerization to its completion, the addition of water duringpolymerization being preferred.

[0065] A polymerization method in which the amount of water is increasedas a phase separation agent during polymerization reaction preferablycomprises a method wherein the polymerization is performed in a processwith at least two steps comprising:

[0066] (I) a first step in which the polymerization is performed in astate where 0.5 to 2.4 moles of water are present per mole of thecharged alkali metal sulfide, at a temperature of 180 to 235° C., toobtain a conversion of the dihalo-aromatic compound of 50 to 98% bymole; and

[0067] (II) a second step in which the polymerization is continued byadding water so as to create a state where 2.5 to 7.0 moles of water arepresent per mole of the charged alkali metal sulfide, and increasing thetemperature to 245 to 290° C.

[0068] The method of the present invention exerts its effect mostsignificantly when water is added during the polymerization process as aphase separation agent to produce a reaction mixture containing a PAShaving a relatively high molecular weight, which is then cooled.

[0069] In the mixture containing a PAS having a relatively highmolecular weight, the molar ratio of water/NMP is within the range ofpreferably from 0.6 to 1.1, more preferably from 0.7 to 1.0, and themolar ratio of NMP/charged alkali metal sulfide is within the range ofpreferably from 2.3 to 5.5, more preferably from 2.5 to 4. Further, themolar ratio of dihalo-aromatic compound/alkali metal sulfide beforestarting the polymerization process is within the range of preferablyfrom 0.9 to 1.2, more preferably from 0.98 to 1.05. The number of molesof the charged alkali metal sulfide (also referred to as “S-component”)is based on the number of moles of the alkali metal sulfide after thecompletion of the dehydration process.

[0070] 2. Cooling Process

[0071] The production process of the present invention provides acooling process for cooling the polymerization reaction systemcomprising a liquid phase containing the product PAS and the organicamide solvent and a vapor phase containing a gas component (A), afterthe polymerization process for PAS, wherein the gas component (A) in thevapor phase is cooled during the cooling process to simultaneouslyreduce the content of a low boiling gas component (A1), which has alower boiling point than water and exists in the gas component (A), inthe vapor phase of the polymerization system.

[0072] The polymerization reaction system at the completion of thepolymerization process is a closed system in a high-temperature andhigh-pressure state. The liquid phase of the polymerization reactionsystem contains organic amide solvents, PAS produced, halogenated alkalimetals (for example, NaCl), unreacted dihalo-aromatic compounds and thelike. Meanwhile, the vapor phase contains a gas component (A) such as,for example, water (water vapor), hydrogen sulfide, nitrogen, oxygen,carbon dioxide, alkyl mercaptans, amines, alkylsulfides, lowerhydrocarbons, unreacted dihalo-aromatic compounds (vapor) and organicamide solvents (vapor).

[0073] These gas components (A) contain, other than those added andmixed in the raw material preparation process, polymerization processand the like, newly produced components such as those produced by thethermal decomposition of organic amide solvents during thepolymerization reaction at high-temperature and high-pressure, by thedecomposition of alkali metal sulfides or by the reaction of hydrogensulfide with other components. For example, when sodium sulfide isallowed to react with p-dichlorobenzene in a polymerizer purged withnitrogen to synthesize polyphenylene sulfide, the gas component (A)contains relatively large amount of nitrogen, hydrogen sulfide, water,methyl mercaptan and the like, and p-dichlorobenzene, NMP, carbondioxide, dimethyl mercaptan and the like are also detected. Note thatthis formulation of the gas component is one example and it variesdepending on the variation of the production conditions. For example, ifthe polymerizer is not purged with nitrogen gas, the content of nitrogencontained in the gas component in the vapor phase will be extremely low.However, even if the production conditions vary, hydrogen sulfide, watervapor and the like will still be contained in relatively large amount inthe vapor phase.

[0074] The gas component (A) contains a large amount of a low boilinggas component (A1) such as hydrogen sulfide, alkyl mercaptans andnitrogen, which has a lower boiling point than water (100° C.). Theselow boiling gas components (A1) cannot be condensed to liquid by aconventional cooling method, so they may be referred to as“non-condensable gas component” in the present specification.

[0075] On the other hand, the gas component (A) contains generallyrelatively small amount of high boiling gas component (A2) with aboiling point equal to or higher than that of water, such as water, NMPand p-dichlorobenzene. The high boiling gas component (A2) is a vaporcomponent (coherent component) that can be condensed to liquid by aconventional cooling method using coolant. Among the high boiling gascomponent (A2), when water (water vapor) is condensed by cooling andrefluxed back into a polymerization reaction system, it is dropped in aliquid phase or reach the liquid phase along a polymerizer wall and isbrought into contact with the high-temperature liquid phase to beevaporated. It has been found that since water absorbs a high latentheat of evaporation from the liquid phase when it is evaporated, theliquid phase is efficiently cooled.

[0076] However, heat transfer is insufficient only by cooling the gascomponent (A) because a large amount of low boiling point component (A1)is contained in the gas component (A) in the vapor phase, and so thehigh boiling point component (A2), the vapor component, cannot beefficiently condensed and refluxed. This will be described now using amethod for cooling the gas component (A) in the vapor phase using areflux condenser as an example.

[0077]FIG. 1 is a sectional view showing a method for cooling a gascomponent in a vapor phase of a polymerization reaction system, using areflux condenser. After a polymerization process, a polymerizationreaction system comprising a liquid phase 2 and a vapor phase 3 isformed in a closed polymerizer 1. A reflux condenser 4 is provided abovethe polymerizer 1. Coolant is passed through a jacket of the refluxcondenser (detail being not shown) from a line 5 and exhausted from aline 6. A gas component (A) in a vapor phase 3 is introduced into thereflux condenser 4 from a valve 9. A thermometer 7 is mounted at the topof the reflux condenser 4. The exhaust valve 8 provided above the refluxcondenser 4 is closed.

[0078] If the gas component (A) in the vapor phase 3 contains a largeamount of low boiling gas component (A1) (non-condensable gascomponent), the efficiency of heat transfer will be extremely low andthe efficiency of condensation of a high boiling gas component (A2)(vapor component) to liquid will be low, even when the gas component (A)is cooled by passing the coolant through the jacket of the refluxcondenser. Further, when the high boiling gas component (A2) in thereflux condenser 4 starts to condense, the low boiling gas component(A1) accumulated within the reflux condenser 4 prevents the high boilinggas component (A2) from entering into the reflux condenser 4.

[0079] Therefore, the present invention adopts a method for cooling thegas component (A) in the vapor phase and reducing the content of the lowboiling gas component (A1) with a lower boiling point than water in thegas component (A) in the vapor phase of a polymerization reactionsystem, in a cooling process. The method for reducing the content of thelow boiling gas component (A1) in the gas component (A) includes amethod for exhausting it from the polymerization reaction system, amethod for allowing it to be absorbed in a liquid phase and a method incombination thereof.

[0080] A specific example of the method for exhausting the low boilinggas component (A1) from the polymerization reaction system includes amethod in which it is exhausted from the exhaust valve 8 by opening theexhaust valve 8 provided above the reflux condenser 4 shown in FIG. 1.However, if the exhaust valve 8 is opened with no contrivance, the highboiling gas component (A2) containing water is also exhausted from thesystem together with the low boiling gas component (A1). Therefore, itis preferable to selectively exhaust the low boiling point component(A1) to reduce the content thereof. A more specific method thereofincludes a method in which at least part of the high boiling gascomponent (A2) is condensed by the reflux condenser 4 and the condensateis refluxed back into the polymerization reaction system, thusincreasing the concentration of the low boiling gas component (A1) inthe upper part of the reflux condenser 4 before exhausting the lowboiling gas component (A1) from the polymerization reaction systemthrough the exhaust valve 8.

[0081] More specifically, after the polymerization process, heating tothe polymerizer 1 is stopped and coolant is passed through the jacket ofthe reflux condenser 4 to start cooling of the gas component (A). Theexhaust valve 8 is left closed. As the cooling is continued, theconcentration of the low boiling gas component (A1) in the refluxcondenser 4 will be increased. Then, the exhaust valve 8 is graduallyopened and the low boiling gas component (A1) is exhausted from thesystem. The exhaust valve may be opened at the same time as the start ofcooling by the reflux condenser, but in this case the valve is desirablygradually opened in a sufficiently long time. The exhaust of the lowboiling gas component (A1) can be determined using the temperatureindicated by the thermometer 7 mounted at the top of the refluxcondenser 4 as an index. Namely, while the low boiling gas component(A1) is exhausted, the temperature indicated by the thermometer (outlettemperature) is low, for example, about 165° C. When the concentrationof the low boiling gas component (A1) in the gas component (A) issignificantly reduced and the high boiling gas component (A2) starts tobe exhausted from the exhaust valve 8, the outlet temperature indicatedby the thermometer will rise, for example, to 236° C. and condensatewill start to be observed at the exhaust port. The exhaust valve 8 isclosed at this point of time. This operation is performed once perbatch, but may be performed two or more times as necessary. Further, thevalve 9 provided in the line connecting the polymerizer 1 and the refluxcondenser 4 may be opened after the polymerization process or left openduring the polymerization process.

[0082] Thus, when the content of the low boiling gas component (A1) inthe vapor phase 3 is reduced, the efficiency of heat transfer of thereflux condenser (heat exchanger) to the high boiling gas component (A2)is significantly enhanced to efficiently condense the high boiling gascomponent (A2) containing water in the reflux condenser 4 and reflux thecondensate back into the polymerizer 1. The refluxed condensate such aswater is introduced into the liquid phase 2. Typically, the condensatesuch as water is refluxed back into the polymerizer from the refluxcondenser 4 and dropped on the liquid phase. The condensate,particularly water, introduced into the liquid phase that is still in ahigh-temperature state is heated by the liquid phase 2 to bere-evaporated. At this time, a high latent heat of evaporation of waterreduces the temperature of the liquid phase 2.

[0083] The method for cooling the gas component (A) in the vapor phaseis not limited to a method using a reflux condenser. External cooling orinternal cooling can be used for cooling the gas component (A) in thevapor phase. For example, a method may be used in which coolant ispassed through an internal coil provided in the vapor phase of thereactor or through an external coil in the upper part of the reactor.When a reflux condenser is not used, an exhaust port and an exhaustvalve for the low boiling gas component (A1) can be provided at the topof a polymerizer. For exhausting the low boiling gas component (A1) fromthe system, it is preferable to use a reflux condenser in which the lowboiling gas component (A1) is easily accumulated.

[0084] Significant improvement of the efficiency of heat transferaccording to the method of the present invention eliminates thenecessity to largely reduce the temperature of coolant (for example,cooling water) to be passed through a jacket of a reflux condenser orthe like. Therefore, it is possible to prevent the deposition ofdihalo-aromatic compounds in a vapor phase on a reflux condenser, aninner wall of a polymerizer or an inner coil by adjusting thetemperature of the coolant in the range from higher than the meltingpoint of the dihalo-aromatic compounds to lower than 100° C. Whenp-dichlorobenzene is used, the temperature of the coolant is morepreferably adjusted around 55 to 70° C. If the deposition of thedihalo-aromatic compound is very improbable, the temperature of thecoolant may be set lower than the above. Further, the temperature of thecoolant may be changed during cooling.

[0085] A collection device storing an aqueous alkali metal hydroxidesolution therein is preferably connected to the exhaust valve 8 locatedabove the reflux condenser 4, and the low boiling gas component (A1)exhausted through the exhaust valve is bubbled into the aqueous solutionto collect at least part of the low boiling gas component (A1) in theaqueous solution. According to this method, hydrogen sulfide in the lowboiling gas component (A1) is collected.

[0086] The method for reducing the low boiling gas component (A1) in thevapor phase includes a method for allowing it to be absorbed in theliquid phase besides the above described method for exhausting it fromthe system. Specifically, addition of alkali metal hydroxides such assodium hydroxide allows hydrogen sulfide in the low boiling gascomponent (A1) to be absorbed and immobilized as sulfides in the liquidphase. The alkali metal hydroxides are preferably added in the liquidphase as an aqueous solution or a mixture with water.

[0087] Addition of alkali metal hydroxides in the liquid phase increasesthe efficiency of heat exchange (coefficient of heat transfer) of thevapor component in the inner coil and external coil provided in thevapor phase of the reactor or the reflux condenser provided above thereactor. Therefore, a preferred amount of alkali metal hydroxides to beadded is the amount that substantially no increase of the efficiency ofheat exchange (coefficient of heat transfer) is observed. However, theamount of alkali metal hydroxides to be added can be increased withinthe range where the quality of the product is not adversely affected.

[0088] The absorption and immobilization of hydrogen sulfide in theliquid phase according to the above method alone largely improves theefficiency of heat transfer to the high boiling gas component (A2) andallows efficient condensation and reflux. Further, the content of thelow boiling gas component (A1) in the vapor phase can be reduced byallowing at least part of the low boiling gas component (A1) to beabsorbed in the liquid phase, and exhausting a residual low boiling gascomponent (A1) from the polymerization reaction system.

[0089] Water, dihalo-aromatic compounds and organic amides which aresubjected to condensation and reflux are not removed from the reactorduring the cooling process, but may be removed after the completion ofthe cooling process. Hydrogen sulfide in the low boiling gas component(A1) (non-condensable gas component) can be recovered and recycled. Theoperation for reducing the low boiling gas component (A1) in the vaporphase may be performed either by a batch operation in one or more timesor by a continuous operation.

[0090] According to the present invention, the reduction of the lowboiling gas component (A1) (non-condensable gas component) in the vaporphase dramatically increases the amount of heat transfer to the highboiling gas component (A2) (vapor component) in the vapor phase, and theeffect of the heat removal by condensation and reflux allows cooling ofthe entire polymerization system including the liquid phase in a shorttime. The PAS obtained by the production method of the present inventionis superior to conventional methods in terms of yield, quality andoperability in washing, filtration and drying processes.

[0091] The cooling after the polymerization process, which is a coolingoperation under high temperature and high pressure, can be performedgenerally by a reactor provided with a reaction vessel jacket, aninternal heat exchanger, an external heat exchanger and the like, and aheat exchanger provided above the reactor. The cooling of the liquidphase may be performed in addition to the cooling of the gas component(A) in the vapor phase. The end point of the exhaust of the low boilinggas component (A1) (non-condensable gas component) from the system canbe determined by a rapid increase of the temperature of the exhaust gasafter passing through the heat exchanger (reflux condenser) provided inthe vapor phase and easy solidification or liquefaction of condensingcomponents in the exhaust gas, as described above.

[0092] In the cooling process, in the case of PPS, a gradual coolingaccording to the above described method is used to reduce thetemperature of the liquid phase to about 155° C. This coolingtemperature allows the PAS produced to become a granular solid and theliquid phase to become slurry. After this, the vapor phase may bereleased from the system; the liquid phase may be rapidly cooled; orwater may be introduced into the liquid phase.

[0093] 3. Recovery Process

[0094] After the cooling process, a washing process, a filtrationprocess, a drying process and the like can be performed according tocommon procedures to recover a purified PAS. For example, a purified PAScan be obtained by separating the slurry of a cooled liquid phase byfiltration as it is or after diluted with water. After the separation byfiltration and screening, the PAS may be subjected to washing treatmentwith the same organic amide solvent as the one in polymerization, otherorganic solvents such as ketones and alcohols, hot water and the like.The PAS may also be treated with acid and salt such as ammoniumchloride. According to the present invention, the PAS can be obtained ina granular form, so the treatment such as filtration, washing, drying orthe like is easy.

[0095] The PAS obtained by the production method of the presentinvention can be molded to various injection moldings and extrusionmoldings such as sheets, films, fibers and pipes, singly or compoundedwith inorganic fillers, fibrous fillers and various synthetic resins.

EXAMPLES

[0096] Hereinafter, the present invention will be more specificallydescribed with reference to examples and comparative examples, but thepresent invention is not limited to these examples.

[0097] In the examples and comparative examples, the “product” meansgranular PPS obtained through the cooling process, washing process,filtration process for collecting granular polymers by a screen with anaperture of 150 μm (100 meshes) and drying process, after the completionof polymerization process.

[0098] The yield of the product was determined based on the theoreticalvalue in the case where all of the sodium sulfide in the autoclave aftersubjected to dehydration process arranged in the former step of thepolymerization process is reacted with p-dichlorobenzene to be convertedto PPS.

Example 1

[0099] A Method for Removing Heat by Condensing and Refluxing VaporComponents after Purging Non-Condensable Gases

[0100] 1. Dehydration Process

[0101] A 20 liter autoclave (polymerizer) with an agitator is providedwith an electric heater for allowing conduction heating from a side walland a thermometer and a pressure gauge for detecting internaltemperature and pressure respectively. A cylindrical reflux condenserwith an inner diameter of 20 mm and a height of 250 mm is installedabove the autoclave in an upright position.

[0102] Into the autoclave, 6,000 g of NMP and 3,800 g of sodium sulfidepentahydrate were charged, purged with nitrogen gas and allowed togradually increase to a temperature of 200° C. while agitated, allowingevaporation of 1,650 g of water and 1,100 g of NMP. At this time, 0.50mole of hydrogen sulfide (H₂S) was also evaporated. Sodium sulfide afterthe dehydration process were 22.04 moles.

[0103] Then, the autoclave was cooled to 180° C., and was added with3,435 g of p-dichlorobenzene (abbreviated as “pDCB”) {pDCB/Na₂S=1.06(molar ratio)}, 2,815 g of NMP, 183 g of water {total water in theautoclave/Na₂S=1.40 (molar ratio)} and 13.3 g of sodium hydroxide of 97%purity so that the amount of sodium hydroxide becomes 6.00% by molerelative to sodium sulfide in addition to 1.00 mole of sodium hydroxideproduced in the reactor by the evaporation of 0.5 mole of hydrogensulfide.

[0104] 2. Polymerization Process

[0105] The reactants were allowed to react at 220° C. for 4.5 hourswhile agitated with the agitator of the autoclave. Then, whilecontinuing agitation, 457 g of water as a phase separation agent wasinjected into the autoclave {total water in the autoclave/Na₂S=2.55(molar ratio)} and the reactants were raised to a temperature of 255° C.and allowed to react for 2.0 hours. The pressure inside the autoclave atthe completion of polymerization was 1.75×10⁶ Pa (gauge pressure). Thetime required in the polymerization process was 6.5 hours.

[0106] 3. Cooling Process

[0107] After the completion of the polymerization, the power of theheater was turned off, and the gas outlet of the exhaust valve attachedto the top of the reflux condenser was connected to a collection devicewith 200 g of a 5% aqueous sodium hydroxide solution therein. Beforepurging gas (exhausting gas components from the system), cooling water(about 60° C.) was passed through a jacket of the reflux condenser tostart cooling.

[0108] Immediately after the above, the gas purge was performed over a2-minute period by gradually opening the exhaust valve attached to thetop of the reflux condenser. The temperature at the gas outlet of thecondenser, which was 165° C. at the start of the gas purge, reached 236°C. at the completion of the gas purge. At this time, the temperatureinside the autoclave was 243° C. and the pressure inside the autoclavewas 1.37×10⁶ Pa. Comparison of this value with the pressure at the sametemperature in the case of no gas purge in Comparative Example 1 to bedescribed below shows that the difference of the pressure inside theautoclave by the gas purge at this temperature corresponds to 0.07×10⁶Pa.

[0109] The time when the condensate was observed at the gas outlet ofthe reflux condenser was defined as the end point of the purge of thelow boiling gas component (A1) (non-condensable gas component). Theweight increase by the collected component absorbed in 200 g of a 5%aqueous sodium hydroxide solution was 1.2 g. In the collected component0.46 g of hydrogen sulfide was detected. However, NMP andp-dichlorobenzene were not detected.

[0110] After the low boiling gas component (A1) was exhausted from thesystem, the exhaust valve of the reflux condenser was closed. Thecondensation and reflux of the high boiling gas component (A2) presentin the vapor phase was further continued by cooling the gas component(A) in the vapor phase. In the cooling process, it took 44 minutes tocool the temperature of the liquid phase from 255° C. to 155° C. Thepressure inside the autoclave at this time was 0.11×10⁶ Pa.

[0111] 4. Recovery Process

[0112] The obtained reaction mixture (liquid phase component) was addedwith acetone, and was washed and filtered three times respectively.Then, water at room temperature was added and washing was repeated fourtimes. The thus obtained slurry was added with an aqueous acetic acidsolution, and was washed and filtered. Further, washing was repeatedfour times, followed by recovering solids with a sieve.

[0113] The obtained wet resin was dried at 105° C. for 13 hours using atray drier. The yield of PPS after drying was 2,169 g (91%).

Example 2

[0114] A Method for Removing Heat by Condensing and Refluxing VaporComponents While Immobilizing the Non-Condensable Gas in the LiquidPhase with a Mixture of Sodium Hydroxide and Water Added in the LiquidPhase

[0115] In Example 1, a mixture of 100 g of sodium hydroxide and 200 g ofwater was injected into the autoclave after polymerization. It tookthree minutes for the injection, and the temperature inside theautoclave became 250° C. and the pressure inside the autoclave became1.52×10⁶ Pa. After the completion of the injection, cooling was startedby passing cooling water through the jacket of the reflux condenser. Inthis manner, the low boiling gas component (A1) was absorbed andimmobilized from the vapor phase into the liquid phase, and at the sametime the condensation and reflux of the high boiling gas component (A2)was continued. The operation after the cooling was performed in the samemanner as in Example 1, and dry PPS was recovered. In this method, thetime required for reaching 155° C. from the start of the cooling of theliquid phase was 48 minutes. The pressure inside the autoclave at thistime was 0.07×10⁶ Pa.

Comparative Example 1

[0116] A Method for Removing Heat by Condensing and Refluxing VaporComponents Without Purging Non-Condensable Gas and Without Immobilizingit in the Liquid Phase

[0117] Everything was performed in the same manner as in Example 1except that the low boiling gas component (A1) (non-condensable gascomponent) was not exhausted from the system, and dry PPS was recovered.The time required for reaching 155° C. from the start of the cooling ofthe liquid phase (255° C.) was 203 minutes. The pressure inside theautoclave at this time was 0.15×10⁶ Pa. The pressure inside theautoclave at the temperature inside the autoclave of 243° C. was1.44×10⁶ Pa.

Comparative Example 2

[0118] A Method for Removing Heat Only by Ambient Cooling WithoutPassing Cooling Water Through the Condenser for the Purpose ofCondensing and Refluxing Vapor Components, Without PurgingNon-Condensable Gas and Without Immobilizing it in the Liquid Phase

[0119] Everything was performed in the same manner as in Example 1except that the low boiling gas component (A1) (non-condensable gascomponent) was not purged from the autoclave and the cooling water wasnot passed through the jacket of the reflux condenser, and dry PPS wasrecovered. The time required for reaching 155° C. from the start of thecooling of the liquid phase (255° C.) was 272 minutes. The pressureinside the autoclave at this time was 0.15×10⁶ Pa.

Comparative Example 3

[0120] A Method of Cooling Utilizing the Heat of Evaporation by Purginga Large Amount of Gas

[0121] Charge, dehydration and polymerization were performed in the samemanner as in Example 1. After the completion of polymerization, the lowboiling gas component (A1) (non-condensable gas component) was notpurged from the autoclave; cooling water was not passed through thejacket of the reflux condenser; and the system was gradually cooled at acooling rate of 1° C./minute to 200° C. The pressure at the time of 200°C. was 0.47×10⁶ Pa. Degassing was performed by opening the exhaustvalve. The degassing took 10 minutes. The pressure and temperatureinside the autoclave became 0.08×10⁶ Pa and 144° C. respectively. Thetime required for reaching 155° C. from the start of the degassing was 8minutes. The pressure inside the autoclave at 155° C. was 0.11×10⁶ Pa.

Comparative Example 4

[0122] A Method for Removing Heat by Condensing and Refluxing VaporComponents by Passing Cooling Water Through the Condenser, by AddingOnly Water in the Liquid Phase

[0123] In Example 1, 200 g of water was charged into the autoclave afterthe completion of polymerization. It took two minutes for the charge,and the temperature and pressure inside the autoclave became 251° C. and1.77×10⁶ Pa respectively. After the completion of the charge, coolingwater was passed through the jacket of the reflux condenser to startcooling. The operation after the cooling was performed in the samemanner as in Example 1, and dry PPS was recovered. The time required forreaching 155° C. from the start of the cooling was 222 minutes. Thepressure inside the autoclave at this time was 0.18×10⁶ Pa.

[0124] The above results are shown in Table 1. TABLE 1 ExamplesComparative Examples 1 2 1 2 3 4 Cooling time 44 48 203 272 63 222(minutes) From the start of cooling to 155° C. Cooling time 44 51 203272 63 224 (minutes) From the completion of polymerization to 155° C.Yield (%) 91 89 91 91 88 90

INDUSTRIAL APPLICABILITY

[0125] According to the method of the present invention, it has becomepossible to significantly reduce the time required in the coolingprocess by reducing a low boiling gas component (non-condensable gascomponent) in a vapor phase, and condensing a high boiling gas component(vapor component) and refluxing the condensate back into a polymerizer(polymerization reaction system) to cool the entire polymerizationreaction system comprising a liquid phase, using a simple apparatus anda method after the completion of the polymerization process. As aresult, it has been achieved to reduce the time required for producing aPAS. Thus, the present invention provides a method for efficiently andeconomically producing the PAS by rapidly cooling the polymerizationreaction system after the polymerization process of the PAS.

1. A method for producing a poly (arylene sulfide) in which adihalo-aromatic compound and an alkali metal sulfide are polymerized byheating in an organic amide solvent, which comprises: (1) after apolymerization process, providing a cooling process for cooling apolymerization reaction system comprising a liquid phase containing thepoly(arylene sulfide) produced and the organic amide solvent and a vaporphase containing a gas component (A); and (2) in the cooling process,cooling the gas component (A) in the vapor phase and reducing thecontent of a low boiling gas component (A1), which has a lower boilingpoint than water and exists in the gas component (A), in the vapor phaseof the polymerization system.
 2. The production method according toclaim 1, wherein the low boiling gas component (A1) contains hydrogensulfide.
 3. The production method according to claim 1, wherein in thecooling process, the gas component (A) in the vapor phase is cooled tocondense a high boiling gas component (A2) with a boiling point equal toor higher than water and reflux the condensate back into thepolymerization reaction system, wherein the high boiling gas component(A2) includes water vapor, an unreacted dihalo-aromatic compound and theorganic amide present in the vapor phase, and to exhaust the low boilinggas component (A1) from the polymerization reaction system, reducing thecontent of the low boiling gas component (A1) in the vapor phase.
 4. Theproduction method according to claim 3, wherein in the cooling process,the gas component (A) in the vapor phase is cooled to condense the highboiling gas component (A2) and reflux the condensate back into thepolymerization reaction system, thereby cooling the polymerizationreaction system comprising a liquid phase.
 5. The production methodaccording to claim 4, wherein the condensate refluxed back into thepolymerization reaction system is introduced into the liquid phase, andthe polymerization reaction system comprising the liquid phase is cooledby the latent heat of evaporation required for re-evaporation of atleast part of the condensate introduced into the liquid phase.
 6. Theproduction method according to claim 3, wherein in the cooling process,after the content of the low boiling gas component (A1) in the vaporphase is reduced, the operation in which the gas component (A) in thevapor phase is cooled to condensate the high boiling gas component (A2)and reflux the condensate back into the polymerization system is furthercontinued.
 7. The production method according to claim 3, wherein thegas component (A) in the vapor phase is cooled by a reflux condenserlocated above the vapor phase.
 8. The production method according toclaim 7, wherein the low boiling gas component (A1) is exhausted fromthe polymerization reaction system through an exhaust valve locatedabove the reflux condenser.
 9. The production method according to claim8, wherein the concentration of the low boiling gas component (A1) inthe upper part of the reflux condenser is increased by condensing atleast part of the high boiling gas component (A2) and refluxing thecondensate back into the polymerization reaction system by the refluxcondenser, and then the low boiling gas component (A1) is exhausted fromthe polymerization reaction system.
 10. The production method accordingto claim 8, wherein a collection device storing an aqueous alkali metalhydroxide solution therein is connected to the exhaust valve locatedabove the reflux condenser, and the low boiling gas component (A1)exhausted through the exhaust valve is bubbled into said aqueoussolution to collect at least part of said low boiling gas component (A1)in said aqueous solution.
 11. The production method according to claim7, wherein the reflux condenser has a structure comprising a jacketthrough which coolant is passed, and the temperature of the coolant tobe passed through the jacket is adjusted from higher than the meltingpoint of the dihalo-aromatic compound to lower than 100° C. to cool thegas component (A).
 12. The production method according to claim 1,wherein the content of the low boiling gas component (A1) in the vaporphase is reduced by allowing at least part of the low boiling gascomponent (A1) to be absorbed in the liquid phase.
 13. The productionmethod according to claim 12, wherein the low boiling gas component (A1)is absorbed in the liquid phase by allowing an alkali metal hydroxide tobe present in the liquid phase to react at least part of the low boilinggas component (A1) with the alkali metal hydroxide in the liquid phase.14. The production method according to claim 12, wherein the content ofthe low boiling gas component (A1) in the vapor phase is reduced byallowing at least part of the low boiling gas component (A1) to beabsorbed in the liquid phase, and exhausting a residual low boiling gascomponent (A1) from the polymerization reaction system.
 15. Theproduction method according to claim 1, wherein in the polymerizationprocess, the dihalo-aromatic compound and the alkali metal sulfide arepolymerized by heating in an organic amide solvent in a polymerizer toproduce a heated and pressurized polymerization reaction systemcomprising a liquid phase heated to a temperature of 200° C. or higher.16. The production method according to claim 1, wherein in thepolymerization process, the dihalo-aromatic compound and the alkalimetal sulfide are polymerized by heating in an organic amide solvent inthe presence of a phase separation agent.
 17. The production methodaccording to claim 16, wherein the phase separation agent is water. 18.The production method according to claim 1, wherein in thepolymerization process, the polymerization is performed in a processwith at least two steps comprising: (I) a first step in which thepolymerization is performed in a state where 0.5 to 2.4 moles of waterare present per mole of the charged alkali metal sulfide, at atemperature of 180 to 235° C., to obtain a conversion of thedihalo-aromatic compound of 50 to 98% by mole; and (II) a second step inwhich the polymerization is continued by adding water so as to create astate where 2.5 to 7.0 moles of water are present per mole of thecharged alkali metal sulfide, and increasing the temperature to 245 to290° C.
 19. The production method according to claim 1, wherein a phaseseparation agent is added to the polymerization reaction system afterthe polymerization process and before the cooling process.
 20. Theproduction method according to claim 1, wherein the poly(arylenesulfide) produced is recovered from the liquid phase after the coolingprocess.